The engine of an automobile is designed to circulate the oil for lubrication and cooling of various components mounted on the engine. Such an engine is provided with an oil pump for circulating the oil and a relief valve for preventing the oil pressure (hereinafter, referred to as “hydraulic pressure”) from being excessively raised by the oil pump.
Korean Patent Application Publication No. 2011-0056811 (May 31, 2011) discloses an oil pump including a relief valve 20.
Referring to FIG. 5, a conventional oil pump 1 includes a housing 10 having a transport path 12 therein, and a relief valve 20 installed on the transport path 12. According to the structure of the oil pump 1, the oil introduced into a lower portion of the housing 10 is transported along the transport path 12, compressed at a predetermined pressure in the transport process, and is then discharged through the side surface of the housing 10. The relief valve 20 installed on the transport path 12 discharges part of the transported oil to the outside when the discharged hydraulic pressure excessively rises. That is, when the discharged hydraulic pressure becomes equal to or higher than a set pressure, the relief valve 20 is operated to open the drain port 22 to discharge a part of the oil.
The oil pump 1 having the above-described structure is operated by a camshaft, and accordingly when the revolutions per minute (rpm) of the engine rises, the hydraulic pressure discharged from the oil pump 1 also rises. Accordingly, the hydraulic pressure circulated in the engine is not maintained to be constant, and lubrication and cooling of various parts such as the cylinder head and the cylinder block are not smoothly performed. In particular, excessive pressure is applied to various parts, thereby causing a significant decrease in durability.
The applicant filed an oil pump control valve (Korean Patent No. 1167505 (Jul. 16, 2012)), which is capable of maintaining a constant hydraulic pressure forcibly transported and discharged from the oil pump to the engine in order to solve the above problems.
The process of hydraulic pressure control by the conventional oil pump control valve will be described below.
When the solenoid is operated, the ball valve is lowered to open an inlet connected to an introduction port, the oil is introduced through the open inlet, and the introduced oil is controlled at a predetermined pressure and then discharged toward the engine through a control port. On the other hand, when the solenoid is stopped, the ball valve rises and closes the inlet, and the oil discharged toward the engine flows into the valve through the control port. At this time, the oil introduced into the valve when the solenoid is stopped is transported to the drain port through a space between a second valve seat and a rod.
Since the through-hole of the second valve seat has a diameter slightly larger than that of the rod so as to guide the movement of the rod, the amount of oil discharged to the space between the second valve seat and the rod is not so large. Therefore, a residual pressure always exists inside the valve, and the ball valve may not operate smoothly due to the residual pressure. In particular, if the operation of the ball valve is not smooth, the hydraulic pressure discharged toward the engine cannot be finely adjusted.
Further, the conventional oil pump control valve has a structure in which the drain port is located at the lower end of the valve. In order to mount the oil pump control valve having such a structure to the outside of the cylinder block, an oil passage needs to be formed at a position adjacent to the outer wall of the cylinder block. However, if the oil passage is positioned close to the outer wall, it is difficult to process the cylinder block, and the thickness of the corresponding portion becomes thin, resulting in poor durability and cracking due to hydraulic pressure.